Inter-image operation apparatus and method and image display apparatus and method

ABSTRACT

An inter-image operation apparatus has temporal subtraction means for calculating a temporal subtraction image from two or more sets of base image data, and history data recording means for recording history data concerning the calculated temporal subtraction image in a database server and concurrently attaching the same history data to the data on the temporal subtraction image. The history data may include information identifying the two or more base images, the date of calculating the temporal subtraction image, the ID number of the patient, the name of the photographed portion of the patient, the photographing angle of the patient, etc. A desired temporal subtraction image may be immediately fetched from the database server by referring to the history data attached thereto if that temporal subtraction image had already been obtained, instead of recalculating that temporal subtraction image. Thus, the diagnostic process of comparing two or more images of an identical object can be carried out efficiently.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an inter-image operation methodand an inter-image operation apparatus for carrying out an inter-imageoperation, and to an image display method and an image display apparatusfor displaying an image obtained by using the above inter-imageoperation method or apparatus. More specifically, the present inventionrelates to an improved method and apparatus for carrying out anoperation between two or more sets of base image data each representinga distinct base image of an identical object, and to an improved methodand apparatus for displaying an image obtained by using the above methodor the apparatus for carrying out the operation.

[0003] 2. Description of the Related Art

[0004] The technique of comparing two or more base images of anidentical object has been used in various fields to discover differencesbetween those base images for, e.g., examining the object based on thedifferences.

[0005] For example, in the field of manufacture, the above technique hasbeen used to search those portions of a product where improvement inendurance is desired by comparing two base images, one being an image ofa new product and the other being an image of the same product after anendurance test, and determining those portions where great differencesare observed between the two base images. In the medical field, asanother example, the technique has been used by doctors to followprogress of disease or stages of a cure and plan the most suitablecourse of treatment by comparing a plurality of radiation images of thesame diseased part of a patient taken at different points in time.

[0006] When using the technique of comparing two or more base images asis used on a daily basis in various fields, those two or more baseimages are often displayed on an image display etc. or outputted onto afilm or the like using a printer. Before displaying or outputting theimages, the images are converted to image density signals or luminancesignals.

[0007] The two or more base images themselves may be displayed oroutputted simply in a row or a column for comparison. However, the pointof the greatest interest for the examiner is the difference between thebase images, and it would be difficult for the examiner to discover aminor difference watching the base images themselves displayed oroutputted in a row or a column.

[0008] In this respect, to improve the efficiency of image comparison,there has been a commonly-used method of extracting and enhancing thedifference between two or more base images by matching positions in thebase images and conducting inter-image operations including asubtraction operation between the images (see, for example, JapanesePatent Application No. 11(1999)-342900). Such a method of extracting andenhancing the difference between the base images helps the examinerrecognize the difference accurately and avoid the risk of overlookingthe progress or cure of the diseased portion.

[0009] However, the inter-image operation as described above isgenerally a quite time-consuming operation because it consists of aseries of operations (e.g., position-matching operations) between anumber of pixels. Moreover, although the image obtained through theinter-image operation (hereinafter, referred to as a processed image) isoften used repeatedly in the course of treatment, the image has usuallybeen recalculated upon each diagnosis. Thus, the examiner has beenrequired to wait for a certain time in each diagnosis until theprocessed image appears on the image display etc., and such a situationhas been an obstacle to efficient diagnosis.

SUMMARY OF THE INVENTION

[0010] One object of the present invention is to provide an inter-imageoperation method and an inter-image operation apparatus for carrying outan inter-image operation, the method and the apparatus workingeffectively in improving efficiency of outputting a processed imageobtained through an inter-image operation between two or more baseimages to be compared of an identical object. Another object of thepresent invention is to provide an improved image display method andapparatus for displaying the processed image obtained by using the aboveinter-image operation method or apparatus.

[0011] The inter-image operation method and apparatus of the presentinvention record history data on the past inter-image operations andoutput the required processed image effectively and appropriatelyreferring to the history data.

[0012] Accordingly, an inter-image operation method according to thepresent invention comprises the steps of carrying out an inter-imageoperation between two or more sets of base image data each representinga distinct base image of an identical object to obtain processed imagedata therefrom, and recording history data on past inter-imageoperations.

[0013] The object of the images herein is not limited to the human bodybut may be of any kind including an animal, a plant, an industrialproduct, a landform, a celestial body or a landscape.

[0014] The inter-image operation preferably includes a subtractionoperation on a pixel-by-pixel basis between the two or more sets of thebase image data. The subtraction operation may be either of a simplesubtraction operation or a weighted subtraction operation. A processedimage obtained through such a subtraction operation is generallyreferred to as a subtraction image. The subtraction image may be, forexample, an energy subtraction image derived through a simplesubtraction operation or a weighted subtraction operation between twooriginal images (i.e., a high energy image (or a normal radiation image)and a low energy image (or a restrained radiation image taken withradiation of restrained energy)) which are taken at substantially thesame point in time but have energy distributions different from eachother, a temporal subtraction image derived from two original imagestaken at different points in time, or a DSA image (digital subtractionangiography image) derived from two original images of a certain bloodvessel taken before and after injection of a contrast medium. Inaddition, it is desirable to carry out a preliminary operation such as aposition-matching operation before carrying out the subtractionoperation. The position-matching operation is preferably carried out bymatching the positions of an anatomical feature area (e.g., an upper endportion of the lung) in the two or more base images.

[0015] Each of the two or more sets of the base image data to beprocessed through the inter-image operation is preferably a set of datarepresenting an original image. The base images may have been taken atdifferent points in time. In addition, each of the two or more sets ofthe base image data may represent a radiation image for medical use.

[0016] The history data on the past inter-image operations may berecorded in a designated recording medium. Instead, the history data maybe attached to the processed image data obtained through the inter-imageoperation, or to each of the two or more sets of the base image dataused for calculating the processed image data. It is also possible touse two or more of the above recording methods in parallel.

[0017] The history data on the past inter-image operations preferablyinclude such data indicating whether or not the processed image data ona certain processed image have already been obtained. In addition, thehistory data on the past inter-image operations preferably includeinformation on recording sites of processed image data obtained in thepast. Then, if it was found by referring to the history data that thedesired set of processed image data had already been obtained, theexaminer would not need to conduct the inter-image operation torecalculate the desired set of the processed image data and would haveonly to fetch and output the desired set of the processed image datastored at the recording site thereof. The time required for fetching andoutputting the stored data is generally shorter than the time requiredfor recalculating the processed image, and thus the present method iseffective in improving the efficiency of diagnosis.

[0018] In the case where the history data is attached to the processedimage data, it is more desirable that the history data of the pastinter-image operations include information identifying the base imageseach represented by one of the two or more sets of the base image dataused for calculating that processed image data, so that identificationof the base images becomes easier and less time-consuming.

[0019] An inter-image operation apparatus according to the presentinvention is designed to carry out the above inter-image operationmethod according to the present invention, and comprises inter-imageoperation means which carries out the inter-image operation between twoor more sets of base image data each representing a distinct base imageof an identical object to obtain processed image data therefrom, andhistory data recording means for recording history data on pastinter-image operations.

[0020] The history data recording means may record the history data onthe past inter-image operations in a designated recording medium.Instead, the history data recording means may attach the history data onthe past inter-image operations to the processed image data obtainedthrough the inter-image operation, or to each of two or more sets of thebase image data used for calculating the processed image data. Thehistory data recording means may also use two or more of the aboverecording methods in parallel.

[0021] The history data on the past inter-image operations preferablyinclude such data indicating whether or not the processed image data ona certain processed image have already been obtained. In addition, thehistory data on the past inter-image operations preferably includeinformation on recording sites of the processed image data alreadyobtained in the past by the inter-image operation means. Then, if theinter-image operation means found by referring to the history data thatthe desired set of processed image data had already been obtained, theexaminer would not need to conduct the inter-image operation torecalculate the desired set of the processed image data and would haveonly to fetch and output the desired set of the processed image datastored at the recording site thereof. The time required for fetching andoutputting the stored data is generally shorter than the time requiredfor recalculating the processed image, and thus the present apparatusworks effectively in improving the efficiency of diagnosis.

[0022] In the case where the history data is attached to the processedimage data, it is more desirable that the history data on the pastinter-image operations include information identifying the base imageseach represented by one of the two or more sets of the base image dataused for calculating that processed image data, so that identificationof the base images becomes easier and less time-consuming.

[0023] Now, exemplary items of the history data and examples of therecording site will be shown in the lists below.

[0024] Exemplary Items of History Data

[0025] The history data may include:

[0026] (1) data indicating whether or not a certain inter-imageoperation has already been done,

[0027] (2) information identifying the two or more base images used inthe inter-image operation, e.g., names or file names for the two or moresets of base image data, the name of the patient, the date of taking thetwo or more base images, an ID number or name of a photographed portionof the patient,

[0028] (3) information identifying the already-obtained processed imagedata, e.g., a name or file name for the processed image data, the nameof the patient, the date of carrying out the inter-image operation, theID number or name of photographed portions of the patient,

[0029] (4) information on the recording sites of the two or more sets ofbase image data used in the inter-image operation or the recording siteof the processed image data,

[0030] (5) data providing detail of the inter-image operation which mayinclude, in the case of the subtraction operation, a size and positionfor each ROI, the number of ROIs, target recognition results, etc.,

[0031] (6) data providing detail of post-processing applied to theprocessed image, e.g., image density conversion characteristics,contrast of the image, brightness of the image, degree of dynamic rangecompression or sharpness of the image, and

[0032] (7) information on the number or detail of a series of processedimages (e.g., temporal subtraction images) for the identical patient orbase images thereof (e.g., base images taken at different points intime).

[0033] Examples of Recording Site

[0034] (A) The history data may be recorded in the designated recordingmedium. Any of the exemplary items (1)-(7) listed above may be recordedin this style.

[0035] (B) The history data may be attached to the processed image data(wherein the designated recording medium may be used in parallel). Theexemplary items (2), (4) (only if the information on the recording sitesof the two or more sets of base image data were included), (5), (6) and(7) may be recorded in this style.

[0036] (C) The history data may be attached to each of two or more setsof base image data representing the base images to be processed throughthe inter-image operation (wherein the designated recording medium maybe used in parallel). Any of the exemplary items (1)-(7) may be recordedin this style. Note that the exemplary item (2) or (4) would onlyinclude information identifying the paired base image or information onthe recording site of the paired base image, respectively, in this case.

[0037] The inter-image operation carried out by the inter-imageoperation means preferably includes a subtraction operation on apixel-by-pixel basis between the two or more sets of the base imagedata.

[0038] Each of the two or more sets of the base image data to beprocessed through the inter-image operation may represent a radiationimage for medical use. In addition, each of the two or more sets of thebase image data is preferably a set of data representing an originalimage. The base images are preferably, but not limited to, images takenat different points in time. Instead, the original images may be two ormore images which are taken at substantially the same point in time buthave energy distributions different from each other (i.e., the imagesused for deriving an energy subtraction image), or may be two originalimages of a certain blood vessel taken before and after injection of acontrast medium (i.e., the images used for deriving a DSA image).

[0039] According to the inter-image operation method and apparatus ofthe present invention, a desired set of the processed image dataobtained in the past may be fetched and outputted at any time byreferring to the recorded history data.

[0040] That is to say, the examiner may check whether or not the desiredprocessed image data has already been obtained by referring to therecorded history data at any time, and may replace the costly step ofrecalculating the desired processed image data with a simple step offetching the desired processed image data if it was found that thedesired processed image data had already been obtained. Thus, it becomespossible to output the desired processed image effectively andappropriately. Concurrently, in the case where it was found that thedesired processed image data had not been obtained yet, it is alsopossible to calculate the desired processed image data through theinter-image operation and store the calculated processed image datatogether with the history data thereof.

[0041] In addition, it helps the examiner easily identify the baseimages and record the information identifying the base images as a partof the history data.

[0042] The data providing the detail of the inter-image operation would,when chosen as an item of the history data, enable the examiner to carryout an experimental inter-image operation choosing a set of parametersdifferent from that for the already-obtained processed image and checkthe result. Accordingly, it becomes much easier for the examiner toobtain a variety of reference images or to determine the mostappropriate set of parameters.

[0043] The image display method and apparatus of the present inventiondisplay the processed image obtained by using the above inter-imageoperation method or apparatus on a display together with the historydata such as the information identifying the two or more base imagesthereof. That is to say, the image display method and apparatus of thepresent invention help the examiner recognize the base images etc. ofthe processed image by providing the examiner with the history data onthe processed image immediately and effectively.

[0044] Accordingly, an image display method according to the presentinvention comprises the steps of displaying an image on a prescribedimage display, the image being a processed image represented byprocessed image data obtained using the above inter-image method orapparatus, and displaying information identifying the two or more baseimages used in the inter-image operation together with the processedimage.

[0045] An image display apparatus according to the present inventioncomprises means for displaying an image on a prescribed image display,the image being a processed image represented by processed image dataobtained using the above inter-image operation method or apparatus, andmeans for displaying information identifying the two or more base imagesused in the inter-image operation together with the processed image.

[0046] According to the image display method and apparatus of thepresent invention, the processed image obtained by using the aboveinter-image operation method or apparatus is displayed together with thehistory data including the information identifying the two or more baseimages used for the inter-image operation. That is to say, the imagedisplay method and apparatus of the present invention help the examineridentify the base images etc. of the processed image by providing theexaminer with the history data on the processed image immediately andeffectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 illustrates one embodiment of an inter-image operationapparatus according to the present invention,

[0048]FIGS. 2A and 2B show an example of a pair of original images usedby the apparatus shown in FIG. 1 to derive a temporal subtraction image,

[0049]FIG. 3 schematically illustrates an overall process of temporalsubtraction,

[0050]FIG. 4 illustrates the concept of a global matching operation,

[0051]FIG. 5 illustrates the concept of a local matching operation,

[0052]FIG. 6 illustrates the concept of a non-linear warping transformoperation, and

[0053]FIGS. 7A, 7B and 7C show an example of a first transformed imageP1″, an (n+1)th original image P(n+1) and a first subtraction imagePsu1, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Now, embodiments of the inter-image operation method andapparatus according to the present invention will be described withreference to the accompanying drawings.

[0055]FIG. 1 illustrates a medical image network 100 including aninter-image operation apparatus 10 which is one embodiment of theinter-image operation apparatus according to the present invention.

[0056] Connected to the network 100 shown in FIG. 1 are one or moreimage generating apparatuses for generating medical images such as a CT(computerized tomography) apparatus, an MRI (magnetic resonance imaging)apparatus and a CR (computer radiography) apparatus 50, a databaseserver 70 for storing diagnostic medical images of any kind generated bythe image generating apparatuses, an image display apparatus 20 fordisplaying those images stored in the database server 70 or those imagessent directly from the image generating apparatuses, the inter-imageoperation apparatus 10 equipped with temporal subtraction means 11(i.e., one form of inter-image operation means) for conducting atemporal subtraction operation between two or more sets of inputted baseimage data to obtain a temporal subtraction image (i.e., one form ofprocessed image), and so on. A printer 30 or a similar device (notshown) is also connected to the network 100 to output the images handledin the network 100 onto a film etc.

[0057] The CR apparatus 50 is an apparatus for obtaining an image ofradiation which has passed through the object as a digital image, byhaving the radiation which has passed through the object project onto anaccumulation phosphor sheet comprising a stimulable phosphor layer sothat the radiation image of the object is recorded on the accumulationphosphor sheet, and photoelectrically reading the light emitted from theaccumulation phosphor sheet exposed to a laser beam, wherein the amountof light emitted from the accumulation phosphor sheet is in proportionto the amount of radiation energy stored thereon. The CR apparatus ofsuch a kind has been widely used in a variety of medical institutionssuch as hospitals.

[0058] A QA-WS (image quality analyzing workstation) 60 connectedbetween the CR apparatus 50 and the network 100 is a workstation havingseveral functions, including a function of checking the diagnosticmedical image generated by the image generating apparatus such as the CRapparatus 50 described above and a function of sending a request to theimage generating apparatus (e.g., the CR apparatus 50) to re-obtain theimage when necessary. The QA-WS 60 as used in the present embodimentdisplays a digital image P generated by the CR apparatus 50 beforestoring the image in the database server 70 to enable the examiner tocarry out preliminary check of image quality (e.g., image density andimage contrast), extent of the image and so on.

[0059] The image display apparatus 20 has several functions includingnot only a simple display function of displaying the image inputted viathe network 100 as a visible image but also a function as a terminal forinputting a request for, e.g., the subtraction operation between two ormore base images P of the same diseased portion of the same patientwhich are taken at different points in time.

[0060] The inter-image operation apparatus 10 is equipped with thetemporal subtraction means 11, as described above, and history datarecording means 12 for recording history data on the temporalsubtraction image calculated by the temporal subtraction means. Toexplain more specifically, the history data recording means puts thehistory data on the calculated temporal subtraction image into thedatabase server 70 for storage and concurrently attaches the samehistory data to the calculated temporal subtraction image data, whereinthe history data may include information identifying the two or morebase images, the date of calculating the temporal subtraction image, theID number of the patient, the name of the photographed portion of thepatient, the photographing angle of the patient, etc. In the presentembodiment, the history data is attached to the temporal subtractionimage data as a header thereof. However, the history data may instead beattached as a separated history data file. In addition, the history datamay also be attached to each of the two or more sets of base image data.

[0061] The temporal subtraction means 11 searches through the historydata recording means 12 when receiving the request for calculating acertain temporal subtraction image from the image display apparatus 20.Then, if it was found that the requested temporal subtraction image hadalready been obtained in the past, the temporal subtraction means 11would fetch the data on that subtraction image from the database server70 referring to the header thereof and output that subtraction image onthe image display apparatus 20 instead of recalculating the data on therequested subtraction image. On the other hand, if it was found that therequested temporal subtraction image had not been obtained yet, thetemporal subtraction means 11 would calculate the data on the requestedtemporal subtraction image and output that subtraction image on theimage display means. At the same time, the temporal subtraction means 11would also send the calculated data on the temporal subtraction image tothe database server 70 for storage. Concurrently, the history datarecording means 12 would attach the history data to the calculated dataon the temporal subtraction image and also send the same history data tothe database server 70 for storage.

[0062] Now, functions of the inter-image operation apparatus 10 will beexplained in detail in the following.

[0063] It is assumed herein that radiation images P1, P2, . . . , Pn ofthe chest part of a certain patient were taken in advance using the CRapparatus 50, went through the check at the QA-WS 60, were sent to thedatabase server 70 via the network 100, and have been stored in thedatabase server 70. An image Pi with a newer index represents an olderbase image. Also stored in the database server 70 are temporalsubtraction images Psu1, Psu2, . . . , Psu(n−1) calculated by thetemporal subtraction means 11 by conducting the temporal subtractionoperation between the newest base image Pn and each of older base imagesP1, P2, . . . , P(n−1), wherein the temporal subtraction image Psu(i)stands for the temporal subtraction image between Pn and Pi.

[0064] The following describes how the inter-image operation apparatus10 functions when a request for displaying the first base image P1 andthe first temporal subtraction image Psu1 (i.e., the temporalsubtraction image between P1 and Pn) is made at the image displayapparatus 20.

[0065] The request made at the image display apparatus 20 is sent to thetemporal subtraction means 11 in the inter-image operation apparatus 10via the network 100. Then the temporal subtraction means 11 searches forthe history data on the desired temporal subtraction image Psu1 throughthe database server 70.

[0066] In the present embodiment, the first temporal subtraction imagePsu1 has already been obtained and stored in the database server 70 andthus the history data thereon can be found in the database server 70.Thus, the temporal subtraction means 11 fetches the first temporalsubtraction image Psu1 from the database server 70 referring to theheader (i.e., the history data) thereof, and sends the first temporalsubtraction image Psu1 to the image display apparatus 20 for output viathe network 100. Concurrently, the temporal subtraction means 11 alsofetches the first base image P1, which has also been stored in thedatabase 70, and sends the first base image P1 to the image displayapparatus 20 for output.

[0067] The examiner can now examine the first base image P1 and thefirst subtraction image Psu1 displayed together on a display portion ofthe image display apparatus 20. The image display apparatus 20preferably has means for displaying on the display portion theinformation identifying two base images used for deriving the firstsubtraction image Psu1 (i.e., the first base image P1 and the nth baseimage Pn), together with the first subtraction image Psu1 itself. Theimage display apparatus 20 having such means is one of the preferredembodiments of the image display apparatus according to the presentinvention.

[0068] In the manner described above, the inter-image operationapparatus 10 of the present invention enable the examiner to checkwhether or not the desired subtraction image Psu has already beenobtained by referring to the recorded history data, and to replace thecostly step of recalculating the desired subtraction image with a simplestep of fetching the data on the desired subtraction image from thedatabase 70 if it was found that the desired subtraction image hadalready been obtained.

[0069] Now, the following describes how the inter-image operationapparatus 10 functions when a request for displaying the (n+1)th baseimage P(n+1) and the nth temporal subtraction image Psu(n) (i.e., thetemporal subtraction image between P1 and P(n+1)) is made at the imagedisplay apparatus 20 immediately after photographing of the (n+1)th baseimage P(n+1) by the CR apparatus 50 etc.

[0070] In the present embodiment, the (n+1)th base image P(n+1) hasalready gone through the check at the QA-WS 60 and been sent to thedatabase server 70 via the network 100 for storage. However, the nthtemporal subtraction image Psu(n) (i.e., the temporal subtraction imagebetween Pi and P(n+1)) has not been calculated yet, and thus neither thenth temporal subtraction image Psu(n) itself nor the history datathereof is stored in the database 70.

[0071] The request for displaying made at the image display apparatus 20is sent to the temporal subtraction means 11 in the inter-imageoperation apparatus 10 in the same manner as described above. Then thetemporal subtraction means 11 searches for the history data of thedesired temporal subtraction image Psu(n) through the database server70.

[0072] As the image Psu(n) is not stored in the database server 70 andthus the temporal subtraction means 11 cannot find the history data ofthe desired temporal subtraction image Psu(n), the temporal subtractionmeans 11 calculates the desired nth temporal subtraction image Psu(n).The process of calculating the nth temporal subtraction image Psu(n)carried out by the temporal subtraction means 11 will be described indetail in the following.

[0073] First of all, the temporal subtraction means 11 fetches the dataon the (n+1)th base image P(n+1) and the data on the first base image P1from the database server 70 (see FIGS. 2A and 2B).

[0074] As shown in FIGS. 2A and 2B, accurate positions of the targetobject (i.e., the chest part in the present embodiment) in the images P1and P(n+1) hardly match with each other. Therefore, there is a risk ofincorrect subtraction between different organs, e.g., between a boneportion and a soft tissues portion, if the subtraction operation wascarried out on the pixel-by-pixel basis without performingposition-matching.

[0075] To avoid this risk, the temporal subtraction means 11 actuallyconducts the subtraction operation after conducting a position-matchingoperation as illustrated in FIG. 3.

[0076] Thus, the calculation process begins with a global matchingoperation between the first base image P1 and the (n+1)th base imageP(n+1). The global matching operation applies an affine transformoperation to the first base image P1 in order to positionally match thefirst base image P1 to the (n+1)th base image P(n+1), transforming thefirst base image P1 to a first image P1′ as shown in FIG. 4.

[0077] Then, the temporal subtraction means 11 divides the (n+1)th baseimage P(n+1) into a plurality of regions of interest (ROIS) T, in whicha pixel in the center of each ROI(T) is represented by a position (x,y)in the x-y coordinate (see FIG. 5). The temporal subtraction means 11also defines search ROI(R)s in the first image P1′. Each of the searchROI(R)s is defined corresponding to each ROI(T) in the (n+1)th baseimage P(n+1), and is provided with a position (x,y) which is identicalto that of one of the ROI(T)s and an area four times as large as that ofeach ROI(T) (i.e., each dimension of the area is twice as long as thatof each ROI(T)).

[0078] The temporal subtraction means 11 next finds a position where thehighest degree of matching is obtained between the images P1′ and P(n+1)(the position is referred to by (x′,y′), representing a matched positionof the center of an ROI) for each ROI(R) by moving an ROI(T) defined inthe (n+1)th base image P(n+1) within the corresponding research ROI(R)defined in the first image P1′ (in other words, the amount of shift iscalculated for every ROI based on local matching). A standard valuewhich represents the degree of matching may be a value based on theleast square or cross-correlation between the two images.

[0079] Illustrated in FIG. 6 is the amount of shift (Δx, Δ y) (whereinΔx= x′−x and Δy=y′−y) between the two images P1′ and P(n+1) derived foreach pixel (x,y) in the center of an ROI in the manner described above.Then, approximation is carried out using a two-dimensional tenth-orderpolynominal to re-calculate the amount of shift (Δx, Δy) to be appliedto each pixel in the first image P1 from each amount of shift (Δx, Δy)for each pixel (x,y) derived based on local matching. A non-linearwarping transform operation (hereinafter, referred to simply as thewarping operation) is then applied to the first image P1′ to shift theposition of each pixel (x,y) in the first image P1′ in accordance withthe re-calculated amount of shift (Δx,Δy) for the pixel.

[0080] Positions of organs in a first transformed image P1″ obtained bywarping the first image P1′ match quite well to the positions of organsappearing in corresponding pixels in the (n+1)th base image P(n+1) (seeFIG. 7A and 7B). A temporal subtraction image Psu1 (see FIG. 7C), whichcontains very few artifacts due to unmatched borders between the organs,is derived by subtracting first transformed image P1″ from the (n+1)thbase image P(n+1) on a pixel-by-pixel basis. Emerging clearly in thetemporal subtraction image Psu1 is a diseased portion K in the leftlung, which does not exist in the first base image P1 but exists in the(n+1)th base image P(n+1).

[0081] Once the temporal subtraction image Psu1 is obtained, the historydata recording means 12 attaches the history data (e.g., the date ofcalculating the image Psu1 or information identifying the base images PIand P(n+1) for the temporal subtraction image Psu1) to the data on theimage Psu1 as a header thereof and sends the image Psu1 to the databaseserver 70 via the network 100 for storage. On the other hand, theobtained temporal subtraction image Psu1 is also sent to the imagedisplay apparatus 20 and displayed on the display portion thereoftogether with the first base image P1 and the (n+1)th base image P(n+1).The examiner can now examine those three images visually on the displayportion.

[0082] The history data recording means 12 also adds the history data,the data identical to those attached to the data on the temporalsubtraction image Psu1, to a history data file in the database server70. Thus, the examiner may easily check whether or not the temporalsubtraction image Psu1 has already been obtained by searching throughthe history data file in the database server 70 whenever necessary.

[0083] In summary, the inter-image operation apparatus 10 of the presentembodiment outputs a required processed image derived from two or morebase images of an identical object to be compared (e.g., a temporalsubtraction image) in a manner much more efficient than the conventionalone.

[0084] Although the temporal subtraction means 11 in the embodimentdescribed above practices the local matching operation after applyingthe global matching operation to at least one image, the temporalsubtraction means 11 may instead practice only the local matchingoperation skipping the global matching operation. In addition, althoughthe transform operations (e.g., the affine transform operation and thenon-linear warping transform operation) are applied only to the firstbase image PI in the embodiment described above, such transformoperations may also be applied to the (n+1)th base image P(n+1).

[0085] Further, although the inter-image operation apparatus 10 is aseparated apparatus in the above embodiment, the function thereof mayinstead be incorporated in the QA-WS 60 or the image display apparatus20.

[0086] In addition, although the temporal subtraction images, the imagesobtained through a process described mainly in Japanese UnexaminedPatent Publication No. 7(1995)-37074, are selected as the images to becalculated by the inter-image operation apparatus 10 in the aboveembodiment, images of other types can also be obtained using theinter-image operation apparatus and method according to the presentinvention. In other words, an image of any kind may be calculated aslong as base images required for calculating the desired image exist. Aset of images to be displayed on the image display apparatus 20 may alsobe of any kind, e.g., a set including two original images (one highenergy image and one low energy image) which are taken at substantiallythe same point in time but have energy distributions different from eachother and an energy subtraction image derived therefrom, or a setincluding two original images of a blood vessel taken before and afterinjection of a contrast medium and a DSA image derived therefrom. Moregenerally, any set of images may be selected as the images to bedisplayed together on the image display apparatus 20 as long as the setcontains two or more images of the identical object to be compared,whether or not the object is a living body.

[0087] Further, although the examiner is required to specify two baseimages related with the desired inter-image operation according to theabove embodiment, the inter-image operation apparatus 10 may insteadprompt the examiner to specify only one base image and search for thoseheaders indicating the same patient ID number, name of the photographedportion and photographing angle as those of the specified base image. Inthat case, the inter-image operation apparatus 10 may calculate atemporal subtraction image between the specified base image and eachimage fetched from the database server 70 referring to the headerthereof.

[0088] In addition, the patient ID etc. may be inputted at the CRapparatus 50 upon photographing to cause the inter-image operationapparatus 10 to conduct the job of searching for necessary base imagesthrough the database server 70 as a job parallel to the photographingjob carried out by the CR apparatus 50. This enables the inter-imageoperation apparatus 10 to carry out the desired inter-image operationbetween a new image and each of the base images fetched from thedatabase 70 immediately after photographing of the new image, and tosend each processed image obtained through the desired inter-imageoperation to the database server 70 for storage with the history dataattached thereto. Such a style advantageously automates the processes ofcalculating and recording the processed image.

[0089] The image display apparatus 20 may be configured to display amessage notifying that the specified inter-image operation is invalid inthe case where the required set of base images is not found in thedatabase server 70.

[0090] The image display apparatus 20 may display the images in anydisplay style. For example, two base images and one temporal subtractionimage derived therefrom may be displayed together. Alternatively, eitherof a base image taken in the past or a subtraction image derived fromthat base image and the newest base image may be displayed alternatelytogether with the newest base image. It is always preferable to displaythe processed image together with the information identifying the baseimages thereof (e.g., file numbers of the base image files).

[0091] In the case where the images are outputted onto a film etc. bythe printer 30, the display style should be preferably adjusted inaccordance with the size of the film, resolution of the printer 30, etc.For example, it is desirable to arrange the images in rows on the filmin the case where the film is wide. On the other hand, it is better toarrange the images in columns in the case where the film is long.

[0092] In addition, various items of the history data and recordingsites thereof may preferably be selected. Listed below are possibleexamples thereof.

[0093] Exemplary Items of History Data

[0094] The history data may include:

[0095] (1) data indicating whether or not a certain inter-imageoperation has already been done,

[0096] (2) information identifying the two or more base images used inthe inter-image operation, e.g., names or file names for the two or moresets of base image data, the name of the patient, the date of taking thetwo or more base images, an ID number or name of a photographed portionof the patient,

[0097] (3) information identifying the already-obtained processed imagedata, e.g., a name or file name for the processed image data, the nameof the patient, the date of carrying out the inter-image operation, theID number or name of photographed portions of the patient,

[0098] (4) information on the recording sites of the two or more sets ofbase image data used in the inter-image operation or the recording siteof the processed image data,

[0099] (5) data providing detail of the inter-image operation which mayinclude, in the case of the subtraction operation, a size and positionfor each ROI, the number of ROIs, target recognition results, etc.,

[0100] (6) data providing detail of post-processing applied to theprocessed image, e.g., image density conversion characteristics,contrast of the image, brightness of the image, degree of compression orsharpness of the image, and

[0101] (7) information on the number or details of a series of processedimages (e.g., temporal subtraction images) for the identical patient orbase images thereof (e.g., base images taken at different points intime).

[0102] Examples of Recording Site

[0103] (A) The history data may be recorded in the designated recordingmedium. Any of the exemplary items (1)-(7) listed above may be recordedin this style.

[0104] (B) The history data may be attached to the processed image data(wherein the designated recording medium may be used in parallel). Theexemplary items (2), (4) (only if the information on the recording sitesof the two or more sets of base image data were included), (5), (6) and(7) may be recorded in this style.

[0105] (C) The history data may be attached to each of two or more setsof base image data representing the base images to be processed throughthe inter-image operation (wherein the designated recording medium maybe used in parallel) Any of the exemplary items (1)-(7) may be recordedin this style. Note that the exemplary item (2) or (4) would onlyinclude information identifying the paired base image or information onthe recording site of the paired base image, respectively, in this case.

What is claimed is:
 1. An inter-image operation method comprising thesteps of carrying out an inter-image operation between two or more setsof base image data each representing a distinct base image of anidentical object to obtain processed image data therefrom, and recordinghistory data on past inter-image operations.
 2. An inter-image operationmethod according to claim 1 , wherein the history data on the pastinter-image operations are recorded in a designated recording medium. 3.An inter-image operation method according to claim 1 , wherein thehistory data on the past inter-image operations are attached to theprocessed image data obtained through the inter-image operation.
 4. Aninter-image operation method according to claim 1 , wherein the historydata on the past inter-image operations are attached to each of said twoor more sets of the base image data used for calculating the processedimage data.
 5. An inter-image operation method according to claim 1 ,wherein the history data on the past inter-image operations includeinformation identifying the base images each represented by one of saidtwo or more sets of the base image data used for calculating theprocessed image data.
 6. An inter-image operation method according toclaim 5 , wherein the history data on the past inter-image operationsare recorded in a designated recording medium.
 7. An inter-imageoperation method according to claim 5 , wherein the history data on thepast inter-image operations are attached to the processed image dataobtained through the inter-image operation.
 8. An inter-image operationmethod according to claim 5 , wherein the history data on the pastinter-image operations are attached to each of said two or more sets ofthe base image data used for calculating the processed image data.
 9. Aninter-image operation method according to claim 1 , wherein the historydata on the past inter-image operations include such data indicatingwhether or not the processed image data on a certain processed imagehave already been obtained.
 10. An inter-image operation methodaccording to claim 9 , wherein the history data on the past inter-imageoperations are recorded in a designated recording medium.
 11. Aninter-image operation method according to claim 9 , wherein the historydata on the past inter-image operations are attached to the processedimage data obtained through the inter-image operation.
 12. Aninter-image operation method according to claim 9 , wherein the historydata on the past inter-image operations are attached to each of said twoor more sets of the base image data used for calculating the processedimage data.
 13. An inter-image operation method according to claim 9 ,wherein the history data on the past inter-image operations includeinformation on recording sites of the processed image data obtained inthe past, and wherein a desired set of the processed image data storedat the recording site thereof is fetched and outputted instead ofconducting the inter-image operation to recalculate the desired set ofthe processed image data, if it was found by referring to the historydata that the desired set of processed image data had already beenobtained.
 14. An inter-image operation method according to claim 13 ,wherein the history data on the past inter-image operations are recordedin a designated recording medium.
 15. An inter-image operation methodaccording to claim 13 , wherein the history data on the past inter-imageoperations are attached to the processed image data obtained through theinter-image operation.
 16. An inter-image operation method according toclaim 13 , wherein the history data on the past inter-image operationsare attached to each of said two or more sets of the base image dataused for calculating the processed image data.
 17. An inter-imageoperation method according to claim 5 , wherein the history data on thepast inter-image operations include such data indicating whether or notthe processed image data on a certain processed image have already beenobtained.
 18. An inter-image operation method according to claim 17 ,wherein the history data on the past inter-image operations are recordedin a designated recording medium.
 19. An inter-image operation methodaccording to claim 17 , wherein the history data on the past inter-imageoperations are attached to the processed image data obtained through theinter-image operation.
 20. An inter-image operation method according toclaim 17 , wherein the history data on the past inter-image operationsare attached to each of said two or more sets of the base image dataused for calculating the processed image data.
 21. An inter-imageoperation method according to claim 17 , wherein the history data on thepast inter-image operations include information on recording sites ofthe processed image data obtained in the past, and wherein a desired setof the processed image data stored at the recording site thereof isfetched and outputted instead of conducting the inter-image operation torecalculate the desired set of the processed image data, if it was foundby referring to the history data that the desired set of processed imagedata had already been obtained.
 22. An inter-image operation methodaccording to claim 21 , wherein the history data on the past inter-imageoperations are recorded in a designated recording medium.
 23. Aninter-image operation method according to claim 21 , wherein the historydata on the past inter-image operations are attached to the processedimage data obtained through the inter-image operation.
 24. Aninter-image operation method according to claim 21 , wherein the historydata on the past inter-image operations are attached to each of said twoor more sets of the base image data used for calculating the processedimage data.
 25. An inter-image operation method according to any one ofclaims 1-24, wherein the inter-image operation includes a subtractionoperation on a pixel-by-pixel basis between said two or more sets of thebase image data.
 26. An inter-image operation method according to anyone of claims 1-24, wherein each of said two or more sets of the baseimage data is a set of data representing an original image.
 27. Aninter-image operation method according to any one of claims 1-24,wherein the inter-image operation includes a subtraction operation on apixel-by-pixel basis between said two or more sets of the base imagedata, and wherein each of said two or more sets of the base image datais a set of data representing an original image.
 28. An inter-imageoperation method according to any one of claims 1-24, wherein the baseimages each represented by one of said two or more sets of the baseimage data are taken at different points in time.
 29. An inter-imageoperation method according to any one of claims 1-24, wherein theinter-image operation includes a subtraction operation on apixel-by-pixel basis between said two or more sets of the base imagedata, and wherein the base images each represented by one of said two ormore sets of the base image data are taken at different points in time.30. An inter-image operation method according to any one of claims 1-24,wherein each of said two or more sets of the base image data representsa radiation image for medical use.
 31. An inter-image operation methodaccording to any one of claims 1-24, wherein the inter-image operationincludes a subtraction operation on a pixel-by-pixel basis between saidtwo or more sets of the base image data, and wherein each of said two ormore sets of the base image data represents a radiation image formedical use.
 32. An inter-image operation apparatus comprisinginter-image operation means which carries out an inter-image operationbetween two or more sets of base image data each representing a distinctbase image of an identical object to obtain processed image datatherefrom, and history data recording means for recording history dataon past inter-image operations.
 33. An inter-image operation apparatusaccording to claim 32 , wherein the history data recording means recordsthe history data on the past inter-image operations in a designatedrecording medium.
 34. An inter-image operation apparatus according toclaim 32 , wherein the history data recording means attaches the historydata on the past inter-image operations to the processed image dataobtained through the inter-image operation.
 35. An inter-image operationapparatus according to claim 32 , wherein the history data recordingmeans attaches the history data on the past inter-image operations toeach of said two or more sets of the base image data used forcalculating the processed image data.
 36. An inter-image operationapparatus according to claim 32 , wherein the history data on the pastinter-image operations include information identifying the base imageseach represented by one of said two or more sets of the base image dataused for calculating the processed image data.
 37. An inter-imageoperation apparatus according to claim 36 , wherein the history datarecording means records the history data on the past inter-imageoperations in a designated recording medium.
 38. An inter-imageoperation apparatus according to claim 36 , wherein the history datarecording means attaches the history data on the past inter-imageoperations to the processed image data obtained through the inter-imageoperation.
 39. An inter-image operation apparatus according to claim 36, wherein the history data recording means attaches the history data onthe past inter-image operations to each of said two or more sets of thebase image data used for calculating the processed image data.
 40. Aninter-image operation apparatus according to claim 32 , wherein thehistory data on the past inter-image operations include such dataindicating whether or not the processed image data on a certainprocessed image have already been obtained.
 41. An inter-image operationapparatus according to claim 40 , wherein the history data recordingmeans records the history data on the past inter-image operations in adesignated recording medium.
 42. An inter-image operation apparatusaccording to claim 40 , wherein the history data recording meansattaches the history data on the past inter-image operations to theprocessed image data obtained through the inter-image operation.
 43. Aninter-image operation apparatus according to claim 40 , wherein thehistory data recording means attaches the history data on the pastinter-image operations to each of said two or more sets of the baseimage data used for calculating the processed image data.
 44. Aninter-image operation apparatus according to claim 40 , wherein thehistory data on the past inter-image operations include information onrecording sites of the processed image data obtained in the past, andwherein a desired set of the processed image data stored at therecording site thereof is fetched and outputted instead of conductingthe inter-image operation to recalculate the desired set of theprocessed image data, if the inter-image operation means found byreferring to the history data, that the desired set of processed imagedata had already been obtained.
 45. An inter-image operation apparatusaccording to claim 44 , wherein the history data recording means recordsthe history data on the past inter-image operations in a designatedrecording medium.
 46. An inter-image operation apparatus according toclaim 44 , wherein the history data recording means attaches the historydata on the past inter-image operations to the processed image dataobtained through the inter-image operation.
 47. An inter-image operationapparatus according to claim 44 , wherein the history data recordingmeans attaches the history data on the past inter-image operations toeach of said two or more sets of the base image data used forcalculating the processed image data.
 48. An inter-image operationapparatus according to claim 36 , wherein the history data on the pastinter-image operations include such data indicating whether or not theprocessed image data on a certain processed image have already beenobtained.
 49. An inter-image operation apparatus according to claim 48 ,wherein the history data recording means records the history data on thepast inter-image operations in a designated recording medium.
 50. Aninter-image operation apparatus according to claim 48 , wherein thehistory data recording means attaches the history data on the pastinter-image operations to the processed image data obtained through theinter-image operation.
 51. An inter-image operation apparatus accordingto claim 48 , wherein the history data recording means attaches thehistory data on the past inter-image operations to each of said two ormore sets of the base image data used for calculating the processedimage data.
 52. An inter-image operation apparatus according to claim 48, wherein the history data on the past inter-image operations includeinformation on recording sites of the processed image data obtained inthe past, and wherein a desired set of the processed image data storedat the recording site thereof is fetched and outputted instead ofconducting the inter-image operation to recalculate the desired set ofthe processed image data, if the inter-image operation means found byreferring to the history data that the desired set of processed imagedata had already been obtained.
 53. An inter-image operation apparatusaccording to claim 52 , wherein the history data recording means recordsthe history data on the past inter-image operations in a designatedrecording medium.
 54. An inter-image operation apparatus according toclaim 52 , wherein the history data recording means attaches the historydata on the past inter-image operations to the processed image dataobtained through the inter-image operation.
 55. An inter-image operationapparatus according to claim 52 , wherein the history data recordingmeans attaches the history data on the past inter-image operations toeach of said two or more sets of the base image data used forcalculating the processed image data.
 56. An inter-image operationapparatus according to any one of claims 32-55, wherein the inter-imageoperation includes a subtraction operation on a pixel-by-pixel basisbetween said two or more sets of the base image data.
 57. An inter-imageoperation apparatus according to any one of claims 32-55, wherein eachof said two or more sets of the base image data is a set of datarepresenting an original image.
 58. An inter-image operation apparatusaccording to any one of claims 32-55, wherein the inter-image operationincludes a subtraction operation on a pixel-by-pixel basis between saidtwo or more sets of the base image data, and wherein each of said two ormore sets of the base image data is a set of data representing anoriginal image.
 59. An inter-image operation apparatus according to anyone of claims 32-55, wherein the base images each represented by one ofsaid two or more sets of the base image data are taken at differentpoints in time.
 60. An inter-image operation apparatus according to anyone of claims 32-55, wherein the inter-image operation includes asubtraction operation on a pixel-by-pixel basis between said two or moresets of the base image data, and wherein the base images eachrepresented by one of said two or more sets of the base image data aretaken at different points in time.
 61. An inter-image operationapparatus according to any one of claims 32-55, wherein each of said twoor more sets of the base image data represents a radiation image formedical use.
 62. An inter-image operation apparatus according to any oneof claims 32-55, wherein the inter-image operation includes asubtraction operation on a pixel-by-pixel basis between said two or moresets of the base image data, and wherein each of said two or more setsof the base image data represents a radiation image for medical use. 63.An image display method comprising the steps of displaying an image on aprescribed image display, said image being a processed image representedby processed image data obtained by carrying out an inter-imageoperation between two or more sets of base image data each representinga distinct base image of an identical object, and displaying informationidentifying the two or more base images each represented by one of saidtwo or more sets of the base image data together with the processedimage.
 64. An image display apparatus comprising means for displaying animage on a prescribed image display, said image being a processed imagerepresented by processed image data obtained by carrying out aninter-image operation between two or more sets of base image data eachrepresenting a distinct base image of an identical object, and means fordisplaying information identifying the two or more base images eachrepresented by one of said two or more sets of the base image datatogether with the processed image.